1. Field of the Invention
The present invention is of a process for separating hydrocarbons, and, more particularly, of a process which uses zeolites, or molecular sieves, to separate alpha-olefins from internal olefins of the same carbon number.
2. Description of the Prior Art
As is well known in the art, it is often commercially desirable to separate mono alpha-olefins from internal mono olefins having the same number of carbon atoms. Mono alpha-olefins, hereinafter referred to as alpha-olefins, are olefins wherein the single double bond is located between the first and second carbon atoms. Internal mono olefins, hereinafter referred to as internal olefins, are olefins wherein the single double bond is located at a position in the molecular other than between the first and second carbon atoms.
One way to separate an alpha-olefin from the corresponding internal olefins is to take advantage of the boiling point difference of the species and use fractional distillation. However, since the boiling point difference between an alpha-olefin and a corresponding internal olefins is quite small, typically on the order of 0.6 to 10 degrees centigrade, fractional distillation requires a large number of stages and is thus often uneconomical.
It is known in the art to use zeolites, or molecular sieves, to separate 1-butene from the corresponding internal olefins, viz., isobutylene, cis-butene-2, and trans-butene-2. Such a process is taught in U.S. Pat. No. 3,723,561, wherein the separation of butene-1 from other C.sub.4 mono olefins is taught. A feed stream containing the various species is contacted with a Type X or Type Y zeolite containing barium or potassium cations. The butene-1 is preferentially adsorbed onto the zeolite and is thereafter desorbed and recovered as a purified product. U.S. Pat. No. 4,119,768 teaches an improvement of the process wherein the desorption of the butene-1 is achieved using a mixture of hexene-1 and cyclohexene or cyclohexane.
It would be desirable to have a process capable of separating alpha-olefins and the corresponding internal olefins for hydrocarbons of carbon number greater than four.